Biological Macromolecules: Carbohydrates, Lipids, and Nucleic Acids

Section 3.2: Monomers, Polymers, and Chemical Reactions

Monomers vs. Polymers

Biological macromolecules are large molecules formed by joining smaller units called monomers. When monomers are linked together, they form polymers, which are essential for cellular structure and function.

• Monomer: A small, repeating molecular unit that can join with others to form a polymer. Example: glucose, amino acid.

• Polymer: A large molecule composed of many monomers bonded together. Example: starch, protein.

Dehydration Synthesis vs. Hydrolysis

Polymers are formed and broken down by specific chemical reactions:

• Dehydration Synthesis (Condensation): A reaction in which two monomers are joined by removing a water molecule. This forms a covalent bond between the monomers.

• Hydrolysis: A reaction in which a polymer is broken down into monomers by adding a water molecule, breaking the covalent bond.

Equation for Dehydration Synthesis:

$\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Dehydration}} \text{Polymer} + \text{H}_2\text{O}$

Equation for Hydrolysis:

$\text{Polymer} + \text{H}_2\text{O} \xrightarrow{\text{Hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Section 3.3: Carbohydrates

Monosaccharides

Monosaccharides are the simplest carbohydrates, consisting of single sugar units. They serve as energy sources and building blocks for more complex carbohydrates.

• Definition: Simple sugars with the general formula $C_nH_{2n}O_n$ (commonly $C_6H_{12}O_6$ for glucose).

• Functions: Provide immediate energy for cellular processes.

• Examples: Glucose, Fructose, Galactose

Disaccharides

Disaccharides are carbohydrates formed by joining two monosaccharides via a glycosidic bond.

• Definition: Sugars composed of two monosaccharide units.

• Functions: Serve as energy sources and transport forms of sugar in plants.

• Examples: Sucrose (glucose + fructose), Lactose (glucose + galactose), Maltose (glucose + glucose)

• Type of Bond Formed: Glycosidic bond (covalent bond formed during dehydration synthesis)

Polysaccharides

Polysaccharides are large carbohydrates composed of many monosaccharide units. They serve as storage and structural molecules in organisms.

• Definition: Polymers of monosaccharides linked by glycosidic bonds.

• Storage Polysaccharides: Store energy for later use.

  • Examples and Functions:

    • Starch (plants): Energy storage in plant cells.

    • Glycogen (animals): Energy storage in liver and muscle cells.

• Structural Polysaccharides: Provide support and protection.

  • Examples and Functions:

    • Cellulose (plants): Main component of plant cell walls.

    • Chitin (fungi, arthropods): Component of fungal cell walls and exoskeletons of insects.

Section 3.4: Lipids

General Characteristics

Lipids are a diverse group of hydrophobic molecules, including fats, phospholipids, and steroids. They are insoluble in water and serve as energy storage, structural components, and signaling molecules.

• Characteristic Shared: Hydrophobicity (do not dissolve in water)

Fats (Triglycerides)

Fats are lipids composed of glycerol and three fatty acids, forming triglycerides. They store energy and provide insulation.

• Structure of Triglycerides: One glycerol molecule bonded to three fatty acids.

• Type of Bonds: Ester bonds formed between glycerol and fatty acids during dehydration synthesis.

Saturated vs. Unsaturated Fatty Acids

• Saturated Fatty Acids: No double bonds between carbon atoms; solid at room temperature. Example: butter.

• Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature. Example: olive oil.

Function of Fats

• Long-term energy storage

• Insulation and protection of organs

Phospholipids

Phospholipids are major components of cell membranes, consisting of two fatty acids, a glycerol, and a phosphate group.

• Structure: Hydrophilic (water-attracting) phosphate head and hydrophobic (water-repelling) fatty acid tails.

• Function: Form bilayers in cell membranes, creating a barrier between the cell and its environment.

• Behavior in Water: Spontaneously arrange into bilayers with hydrophobic tails inward and hydrophilic heads outward.

Steroids

Steroids are lipids with a characteristic four-ring structure. They function as hormones and structural components.

• Structure: Four fused carbon rings.

• Examples: Cholesterol (component of cell membranes), Testosterone, Estrogen (hormones)

Section 3.5: Nucleic Acids

Structure and Function of a Gene

Nucleic acids (DNA and RNA) store and transmit genetic information. Genes are segments of DNA that code for proteins.

• Gene: A sequence of DNA that contains instructions for building a protein.

The Role of Nucleic Acids

• DNA stores genetic information; RNA helps express genetic information.

The Components of Nucleic Acids

• Monomers: Nucleotides

• Polymers: DNA and RNA

• Structure of a Nucleotide: Phosphate group, pentose sugar (deoxyribose in DNA, ribose in RNA), nitrogenous base (purine or pyrimidine)

• Purines: Adenine (A), Guanine (G)

• Pyrimidines: Cytosine (C), Thymine (T, DNA only), Uracil (U, RNA only)

• Deoxyribose vs. Ribose: Deoxyribose (DNA) lacks one oxygen atom compared to ribose (RNA)

Nucleotide Polymers

• Type of Bonds: Phosphodiester bonds link nucleotides together.

• 5' and 3' Ends: Nucleic acid strands have directionality, with a 5' phosphate end and a 3' hydroxyl end.

• Relationship to Proteins: DNA codes for proteins via RNA intermediates.

Structures of DNA and RNA Molecules

• Structure of DNA: Double helix with two complementary strands.

• Base Pairing Rules: A pairs with T (DNA) or U (RNA); G pairs with C.

• Complementary Strands: Each strand serves as a template for the other.

• Differences between DNA and RNA:

  • DNA: Double-stranded, contains deoxyribose, uses thymine.

  • RNA: Single-stranded, contains ribose, uses uracil.

Feature	DNA	RNA
Strands	Double	Single
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Function	Genetic information storage	Protein synthesis, gene expression